1. Field of the Invention
The present invention pertains to the art of appliances and, more particularly, to a method for maintaining illumination of an display LED of an appliance over an extended period of time.
2. Discussion of the Prior Art
In recent years, certain household appliances have been manufactured with display units for allowing users to select different criteria or read messages displayed by the appliances. Such a display unit is often defined by a liquid crystal display with an array of light emitting diode (LED) backlights.
A drawback of LED backlights is that the output intensity of the backlights decreases steadily with time. Some factors that affect the rate at which an LED's intensity diminishes include the amount of electric current used to drive the LED, the temperature of the environment in which the LED is operated, and the humidity of the environment in which the LED is operated. When LEDs are used in an appliance, the minimum amount of electric current required to drive the LEDs at an acceptable brightness is approximately 10 mA. When the LED is operated in an environment of about 25° C., the relative illumination level is reduced by an average of 50% after 50,000 hours. Since the typical lifetime of a household appliance far exceeds 50,000 hours, supplying current to the LEDs at a constant rate of 10 mA undesirably results in a time varying intensity.
Several attempts and suggestions have been made to solve the problems associated with the deterioration of LEDs over time. For example, it is possible to double the lifetime of LEDs by doubling the number of LEDs and cutting the current supplied to each LED by 50%. However, there are significant costs associated with doubling the number of LEDs used in appliance control panels, which make this option undesirable. Another method of maintaining a consistent output of LEDs over time is to employ a sensor to detect when the LED output begins to diminish and to increase the voltage supplied to the LED based on the output of the sensor. This option may also be cost prohibitive due to the addition and maintenance of the sensor. Therefore, there is a need for a method and arrangement for maintaining the light intensity of LEDs provided in an appliance display without significantly increasing the costs of manufacturing the appliance.